Process for producing flame-retardant porous materials based on polyurea

ABSTRACT

The present invention relates to a process for producing flame-retardant porous materials comprising the following steps:
     (a) reacting at least one polyfunctional isocyanate (a1) and at least one polyfunctional aromatic amine (a2) in an organic solvent optionally in the presence of water as component (a3) and optionally in the presence of at least one catalyst (a5); and then   (b) removing the organic solvent to obtain the organic porous material, where step (a) is carried out in the presence of at least one organic flame retardant as component (a4), where this flame retardant is soluble in the solvent.   

     The invention further relates to the porous materials thus obtainable, and also to the use of the porous materials for thermal insulation.

The present invention relates to a process for producing flame-retardantporous materials comprising the following steps:

-   -   (a) reacting at least one polyfunctional isocyanate (a1) and at        least one polyfunctional aromatic amine (a2) in an organic        solvent optionally in the presence of water as component (a3)        and optionally in the presence of at least one catalyst (a5);        and then    -   (b) removing the organic solvent to obtain the organic porous        material, where step (a) is carried out in the presence of at        least one organic flame retardant as component (a4), where this        flame retardant is soluble in the solvent.

The invention further relates to the porous materials thus obtainable,and also to the use of the porous materials for thermal insulation.

On the basis of theoretical considerations, porous materials, such aspolymer foams, with pores in the size range of a few micrometers ormarkedly less, and with high porosity of at least 70% are particularlygood thermal insulators.

These porous materials with small average pore diameter can by way ofexample take the form of organic xerogels. The term xerogel is not useduniformly throughout the literature. The term xerogel generally means aporous material which has been produced via a sol-gel process, where theliquid phase has been removed from the gel via drying of the liquidphase below the critical temperature and below the critical pressure(“subcritical conditions”). In contrast to this, the term aerogels isgenerally used when the removal of the liquid phase from the gel takesplace under supercritical conditions.

In the sol-gel process, a sol based on a reactive organic gel precursoris first produced, and then the sol is gelled via a crosslinkingreaction to give a gel. In order to obtain a porous material, such as axerogel, from the gel, the liquid has to be removed. The simplified termdrying is used hereinafter to denote that step.

WO-2008/138978 discloses xerogels comprising from 30 to 90% by weight ofat least one polyfunctional isocyanate and from 10 to 70% by weight ofat least one polyfunctional aromatic amine, where the volume-averagepore diameter of these is at most 5 micrometers.

However, the drying process in the processes known from the prior art,in particular the drying process under subcritical conditions, isattended by shrinkage, with porosity reduction and density increase.

Another problem with the formulations which are known from the prior artand are based on isocyanates and on amines is that the flame retardancyproperties are inadequate for many applications.

It was therefore an object to avoid the abovementioned disadvantages. Inparticular, the intention was to provide a porous material which doesnot have the abovementioned disadvantages or has them to a reducedextent. The porous materials were intended to have advantageous thermalconductivity in vacuo. A further intention was that the porous materialsalso have low thermal conductivity at pressures above the vacuum range,in particular within a pressure range from about 1 mbar to about 100mbar. This is desirable since a pressure increase occurs in vacuumpanels over the course of time. A further intention was that the porousmaterials also have advantageous thermal conductivities in the aeratedcondition, i.e. at atmospheric pressure. A further intention was thatthe porous material simultaneously have high porosity, low density, andadequately high mechanical stability, together with advantageous flameretardancy properties.

The intention was to discover a process which gives porous organicmaterials with improved flame retardancy properties. At the same time,the intention was that the materials have an advantageous porestructure, so that abovementioned advantages are retained. The shrinkageoccurring on removal of the solvent from the gel product obtained shouldbe minimized, in particular when the solvent is removed undersubcritical conditions.

The process of the invention and the porous materials thus obtainablewere accordingly discovered.

The process of the invention for producing a porous material comprisesthe following steps:

-   -   (a) reacting at least one polyfunctional isocyanate (a1) and at        least one polyfunctional aromatic amine (a2) in an organic        solvent optionally in the presence of water as component (a3)        and optionally in the presence of at least one catalyst (a5);        and then    -   (b) removing the organic solvent to obtain the organic porous        material, where step (a) is carried out in the presence of at        least one organic flame retardant as component (a4), where this        flame retardant is soluble in the solvent.

An organic flame retardant is an organic compound which is at the sametime a flame retardant. An organic compound is a compound whichcomprises at least one carbon atom.

A flame retardant is a compound or a mixture of a plurality of compoundswhich improves the flame retardancy properties of the resultant porousmaterials. For the purposes of the present invention, flame retardancyproperties are characterized via the BKZ test. The term BKZ test meansthe determination of the fire index (combustibility class and fumeclass) as in “Wegleitung für Feuerpolizeivorschriften: Baustoffe andBauteile” [Guidelines for Fire Authority Regulations: ConstructionMaterials and Components], Part B: Prüfbestimmungen [Test Procedures],1988 edition (with 1990, 1994, and 1995 addendums) of the VereinigungKantonaler Feuerversicherungen (VKF) [Association of Swiss Cantonal FireInsurers]. A flame retardant is preferably characterized in that itleads to a combustibility class of 5 for the resultant porous materialsin the BKZ test.

Preferred embodiments can be found in the claims and the description.Combinations of preferred embodiments are within the scope of thisinvention. Preferred embodiments of the components used are firstexplained below.

The polyfunctional isocyanates (a1) are hereinafter together termedcomponent (a1). Correspondingly, the polyfunctional aromatic amines (a2)are hereinafter together termed component (a2). It is obvious to theperson skilled in the art that the monomer components mentioned arepresent in reacted form in the porous material.

For the purposes of the present invention, the term functionality of acompound means the number of reactive groups per molecule. In the caseof monomer component (a1), the functionality is the number of isocyanategroups per molecule. In the case of the amino groups of monomercomponent (a2), the term functionality means the number of reactiveamino groups per molecule. The functionality of a polyfunctionalcompound here is at least 2.

If component (a1) and/or (a2) use(s) a mixture made of compounds havingdifferent functionality, the functionality of the components is therespective number average functionality of the individual componunds. Apolyfunctional compound comprises at least two of the abovementionedfunctional groups per molecule.

Component (a1)

The process of the invention reacts at least one polyfunctionalisocyanate as component (a1).

For the purposes of the process of the invention, the amount used ofcomponent (a1) is preferably at least 20% by weight, in particular atleast 30% by weight, particularly preferably at least 40% by weight,very particularly preferably at least 55% by weight, in particular atleast 68% by weight, based in each case on the total weight ofcomponents (a1) to (a4), which is 100% by weight. For the purposes ofthe process of the invention, the amount used of component (a1) ismoreover preferably at most 99.8% by weight, in particular at most 99.3%by weight, particularly preferably at most 97.5% by weight, based ineach case on the total weight of components (a1) to (a4), which is 100%by weight.

Polyfunctional isocyanates that can be used are aromatic, aliphatic,cycloaliphatic, and/or araliphatic isocyanates. These polyfunctionalisocyanates are known per se or can be produced by methods known per se.The polyfunctional isocyanates can also in particular be used in theform of mixtures, in which case component (a1) therefore comprisesvarious polyfunctional isocyanates. Polyfunctional isocyanates that canbe used as monomer units (a1) have two or more than two isocyanategroups per molecule of monomer component (and in the first case arecalled diisocyanates).

Particularly suitable compounds are diphenylmethane 2,2′-, 2,4′-, and/or4,4′-diisocyanate (MDI), naphthylene 1,5-diisocyanate (NDI), tolylene2,4- and/or 2,6-diisocyanate (TDI), 3,3′-dimethyldiphenyl diisocyanate,diphenylethane 1,2-diisocyanate, and/or p-phenylene diisocyanate (PPDI),tri-, tetra-, penta-, hexa-, hepta-, and/or octamethylene diisocyanate,2-methylpentamethylene 1,5-diisocyanate, 2-ethylbutylene1,4-diisocyanate, pentamethylene 1,5-diisocyanate, butylene1,4-diisocyanate,1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane (isophoronediisocyanate, IPDI), 1,4- and/or 1,3-bis(isocyanatomethyl)cyclohexane(HXDI), cyclohexane 1,4-diisocyanate, 1-methylcyclohexane 2,4- and/or2,6-diisocyanate, and dicyclohexylmethane 4,4′-, 2,4′-, and/or2,2′-diisocyanate.

Aromatic isocyanates are preferred polyfunctional isocyanates (a1). Thefollowing embodiments are particularly preferred as polyfunctionalisocyanates of component (a1):

-   -   i) polyfunctional isocyanates based on tolylene diisocyanate        (TDI), in particular 2,4-TDI o r 2,6-TDI, or a mixture made of        2,4- and 2,6-TDI;    -   ii) polyfunctional isocyanates based on diphenylmethane        diisocyanate (MDI), in particular 2,2′-MDI or 2,4′-MDI, or        4,4′-MDI, or oligomeric MDI, which is also termed polyphenyl        polymethylene isocyanate, or a mixture made of two or three of        the abovementioned diphenylmethane diisocyanates, or crude MDI,        which is produced during the production of MDI, or a mixture        made of at least one oligomer of MDI and at least one of the        abovementioned low-molecular-weight MDI derivatives;    -   iii) a mixture made of at least one aromatic isocyanate as in        embodiment i) and at least one aromatic isocyanate as in        embodiment ii).

Oligomeric diphenylmethane diisocyanate is particularly preferred aspolyfunctional isocyanate. Oligomeric diphenylmethane diisocyanate(hereinafter oligomeric MDI) is a mixture made of a plurality ofoligomeric condensates and thus of derivatives of diphenylmethanediisocyanate (MDI). The polyfunctional isocyanates can also preferablybe composed of mixtures of monomeric aromatic diisocyanates and ofoligomeric MDI.

Oligomeric MDI comprises one or more polynuclear condensates of MDIhaving functionality of more than 2, in particular 3 or 4, or 5.Oligomeric MDI is known and is often termed polyphenyl polymethyleneisocyanate, or else polymeric MDI. Oligomeric MDI is usually composed ofa mixture made of MDI-based isocyanates with varying functionality.Oligomeric MDI is usually used in a mixture with monomeric MDI.

The (average) functionality of an isocyanate which comprises oligomericMDI can vary within the range from about 2.2 to about 5, in particularfrom 2.4 to 3.5, in particular from 2.5 to 3. One such mixture ofMDI-based polyfunctional isocyanates having varying functionalities isin particular crude MDI, which is produced during the production asintermediate product in crude MDI production of MDI, usually catalyzedby hydrochloric acid.

Polyfunctional isocyanates or mixtures of a plurality of polyfunctionalisocyanates based on MDI are known and are marketed by way of example asLupranat® by BASF Polyurethanes GmbH.

The functionality of component (a1) is preferably at least two, inparticular at least 2.2, and particularly preferably at least 2.4. Thefunctionality of component (a1) is preferably from 2.2 to 4, andparticularly preferably from 2.4 to 3.

The content of isocyanate groups in component (a1) is preferably from 5to 10 mmol/g, in particular from 6 to 9 mmol/g, particularly preferablyfrom 7 to 8.5 mmol/g. The person skilled in the art is aware of areciprocal relationship between the content of isocyanate groups inmmol/g and the value known as equivalent weight in g/equivalent. Thecontent of isocyanate groups in mmol/g is calculated from the content in% by weight as in ASTM D5155-96 A.

In one preferred embodiment, component (a1) is composed of at least onepolyfunctional isocyanate selected from diphenylmethane4,4′-diisocyanate, diphenylmethane 2,4′-diisocyanate, diphenylmethane2,2′-diisocyanate, and oligomeric diphenylmethane diisocyanate. For thepurposes of this preferred embodiment, component (a1) particularlypreferably comprises oligomeric diphenylmethane diisocyanate, and itsfunctionality is at least 2.5.

The viscosity of component (a1) used can vary widely. The viscosity ofcomponent (a1) is preferably from 100 to 3000 mPa·s, particularlypreferably from 200 to 2500 mPa·s.

Component (a2)

Component (a2) in the invention is at least one polyfunctional aromaticamine.

Component (a2) can to some extent be produced in situ. In this type ofembodiment, the reaction for the purposes of step (a) takes place in thepresence of water (a3). Water reacts with the isocyanate groups to giveamino groups with liberation of CO₂. Polyfunctional amines are thus tosome extent produced as intermediate product (in situ). During a furthercourse of the reaction, they are reacted with isocyanate groups to giveurea linkages.

In this preferred embodiment, the reaction is carried out in thepresence of water and of a polyfunctional aromatic amine as component(a2), and also optionally in the presence of a catalyst (a5).

In another embodiment, likewise preferred, the reaction of component(a1) and of a polyfunctional aromatic amine as component (a2) isoptionally carried out in the presence of a catalyst (a5). No water (a3)is present here.

Polyfunctional aromatic amines are known per se to the person skilled inthe art. The term polyfunctional amines means amines which, permolecule, have at least two amino groups reactive toward isocyanates.Groups reactive toward isocyanates here are primary and secondary aminogroups, where the reactivity of the primary amino groups is generallymarkedly higher than that of the secondary amino groups.

The polyfunctional aromatic amines are preferably binuclear aromaticcompounds having two primary amino groups (bifunctional aromaticamines), or corresponding tri- or polynuclear aromatic compounds havingmore than two primary amino groups, or a mixture made of theabovementioned compounds. Preferred polyfunctional aromatic amines ofcomponent (a2) are in particular isomers and derivatives ofdiaminodiphenylmethane.

The bifunctional binuclear aromatic amines mentioned are particularlypreferably those of the general formula I,

where R¹ and R² can be identical or different and are selected mutuallyindependently from hydrogen and linear or branched alkyl groups havingfrom 1 to 6 carbon atoms, and where all of the substituents Q¹ to Q⁵ andQ¹′ to Q⁵′ are identical or different and are selected mutuallyindependently from hydrogen, a primary amino group, and a linear orbranched alkyl group having from 1 to 12 carbon atoms, where the alkylgroup can bear further functional groups, with the proviso that thecompound of the general formula I comprises at least two primary aminogroups, where at least one of Q¹′, Q³′, and Q⁵′ is a primary aminogroup, and at least one of Q¹′, Q³′, and Q⁵′ is a primary amino group.

In one embodiment, the alkyl groups for the purposes of the substituentsQ of the general formula I are selected from methyl, ethyl, n-propyl,isopropyl, n-butyl, sec-butyl, and tert-butyl. Compounds of this typeare hereinafter termed substituted aromatic amines (a2-s). However, itis likewise preferable that all of the substituents Q are hydrogen, tothe extent that they are not amino groups as defined above (the termused being unsubstituted polyfunctional aromatic amines).

It is preferable that R¹ and R² for the purposes of the general formulaI are identical or different and are selected mutually independentlyfrom hydrogen, a primary amino group, and a linear or branched alkylgroup having from 1 to 6 carbon atoms. It is preferable that R¹ and R²are selected from hydrogen and methyl. It is particularly preferablethat R¹═R²═H.

Other suitable polyfunctional aromatic amines (a2) are in particularisomers and derivatives of toluenediamine. Particularly preferredisomers and derivatives of toluenediamine for the purposes of component(a2) are toluene-2,4-diamine and/or toluene-2,6-diamine, anddiethyltoluenediamines, in particular 3,5-diethyltoluene-2,4-diamineand/or 3,5-diethyltoluene-2,6-diamine.

It is very particularly preferable that component (a2) comprises atleast one polyfunctional aromatic amine selected from4,4′-diaminodiphenylmethane, 2,4′-diaminodiphenylmethane,2,2′-diaminodiphenylmethane, and oligomeric diaminodiphenylmethane.

Oligomeric diaminodiphenylmethane comprises one or more polynuclearmethylene-bridged condensates of aniline and formaldehyde. OligomericMDA comprises at least one, but generally a plurality of, oligomers ofMDA having functionality of more than 2, in particular 3 or 4, or 5.Oligomeric MDA is known or can be produced by methods known per se.Oligomeric MDA is usually used in the form of mixtures with monomericMDA.

The (average) functionality of a polyfunctional amine of component (a2),where this amine comprises oligomeric MDA, can vary within the rangefrom about 2.3 to about 5, in particular 2.3 to 3.5, and in particularfrom 2.3 to 3. One such mixture of MDA-based polyfunctional amineshaving varying functionalities is in particular crude MDA, which isproduced in particular during the condensation of aniline withformaldehyde as intermediate product in production of crude MDI, usuallycatalyzed by hydrochloric acid.

It is particularly preferable that the at least one polyfunctionalaromatic amine comprises diaminodiphenylmethane or a derivative ofdiaminodiphenylmethane. It is particularly preferable that the at leastone polyfunctional aromatic amine comprises oligomericdiaminodiphenylmethane. It is particularly preferable that component(a2) comprises oligomeric diaminodiphenylmethane as compound (a2) andthat its total functionality is at least 2.1. In particular, component(a2) comprises oligomeric diaminodiphenylmethane and its functionalityis at least 2.4.

For the purposes of the present invention it is possible to control thereactivity of the primary amino groups by using substitutedpolyfunctional aromatic amines for the purposes of component (a2). Thesubstituted polyfunctional aromatic amines mentioned, and stated below,hereinafter termed (a2-s), can be used alone or in a mixture with theabovementioned (unsubstituted) diaminodiphenylmethanes (where all Q informula I are hydrogen, to the extent that they are not NH₂).

In this embodiment, Q², Q⁴, Q²′, and Q⁴′ for the purposes of the formulaI described above, inclusive of the attendant definitions, arepreferably selected in such a way that the compound of the generalformula I has at least one linear or branched alkyl group, where thiscan bear further functional groups, having from 1 to 12 carbon atoms inα-position with respect to at least one primary amino group bonded tothe aromatic ring.

It is preferable that Q², Q⁴, Q²′, and Q⁴′ in this embodiment areselected in such a way that the substituted aromatic amine (a2-s)comprises at least two primary amino groups which respectively have oneor two linear or branched alkyl groups having from 1 to 12 carbon atomsin α-position, where these can bear further functional groups. To theextent that one or more of Q², Q⁴, Q²′, and Q⁴′ are selected in such away that they are linear or branched alkyl groups having from 1 to 12carbon atoms, where these bear further functional groups, preference isthen given to amino groups and/or hydroxy groups, and/or halogen atoms,as these functional groups.

It is preferable that the amines (a2-s) are selected from the groupconsisting of 3,3′, 5,5′-tetraalkyl-4,4′-diaminodiphenylmethane, 3,3′,5,5′-tetraalkyl-2,2′-diaminodiphenylmethane, and 3,3′,5,5′-tetraalkyl-2,4′-diaminodiphenylmethane, where the alkyl groups in3,3′, 5 and 5′ position can be identical or different and are selectedmutually independently from linear or branched alkyl groups having from1 to 12 carbon atoms, where these can bear further functional groups.Preference is given to abovementioned alkyl groups methyl, ethyl,n-propyl, isopropyl, n-butyl, sec-butyl or tert-butyl (in each caseunsubstituted).

In one embodiment, one of, a plurality of, or all of, the hydrogen atomsof one or more alkyl groups of the substituents Q can have been replacedby halogen atoms, in particular chlorine. As an alternative, one of, aplurality of, or all of, the hydrogen atoms of one or more alkyl groupsof the substituents Q can have been replaced by NH₂ or OH. However, itis preferable that the alkyl groups for the purposes of the generalformula I are composed of carbon and hydrogen.

In one particularly preferred embodiment, component (a2-s) comprises3,3′, 5,5′-tetraalkyl-4,4′-diaminodiphenylmethane, where the alkylgroups can be identical or different and are selected independently fromlinear or branched alkyl groups having from 1 to 12 carbon atoms, wherethese optionally can bear functional groups. Abovementioned alkyl groupsare preferably selected from unsubstituted alkyl groups, in particularmethyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, and tert-butyl,particularly preferably from methyl and ethyl. Very particularpreference is given to 3,3′,5,5′-tetraethyl-4,4′-diaminodiphenylmethane,and/or 3,3′,5,5′-tetramethyl-4,4′-diaminodiphenylmethane.

The abovementioned polyfunctional amines of component (a2) are known perse to the person skilled in the art or can be produced by known methods.One of the known methods is the reaction of aniline or, respectively, ofderivatives of aniline with formaldehyde, with acidic catalysis.

As explained above, water, as component (a3), can entirely or to someextent replace the polyfunctional aromatic amine, in that it reacts withan amount, which is then calculated in advance, of additionalpolyfunctional aromatic isocyanate of component (a1) in situ to give acorresponding polyfunctional aromatic amine. To the extent that water isused as component (a3), it is preferable to comply with particularparameters as stated hereinafter.

As previously stated, water reacts with the isocyanate groups to giveamino groups, with liberation of CO₂. Polyfunctional amines are thus tosome extent produced as intermediate product (in situ). During thefurther course of the reaction, they are reacted with isocyanate groupsto give urea linkages. The CO₂ formed is not permitted to disrupt thegelling process to the extent that the structure of the resultant porousmaterial is affected undesirably. This results in the preferred upperlimit stated above for water content, based on the total weight ofcomponents (a1) to (a4), where this content is preferably at most 30% byweight, particularly preferably at most 25% by weight, in particular atmost 20% by weight. Another advantage of water content within said rangeis that, after the gelling process, there is no need for any complicateddrying process to remove any residual water.

To the extent that water is used as component (a3), the amount of waterpreferably used is from 0.1 to 30% by weight, in particular from 0.2 to25% by weight, particularly preferably from 0.5 to 20% by weight, basedin each case on the total weight of components (a1) to (a4), which is100% by weight.

The preferred amount of water within the ranges described is dependenton whether a catalyst (a5) is used or not.

In a first variant, which comprises the use of water, the reaction ofcomponents (a1) and (a2) is carried out without the presence of acatalyst (a5). In this first embodiment it has proven advantageous touse from 5 to 30% by weight of water as component (a3), in particularfrom 6 to 25% by weight, particularly preferably from 8 to 20% byweight, based in each case on the total weight of components (a1) to(a4), which is 100% by weight.

For the purposes of this first embodiment, the ratio in whichabovementioned components (a1) to (a3) are used is preferably asfollows, in each case based on the total weight of components (a1) to(a3), which is 100% by weight: from 40 to 94.9% by weight of component(a1), in particular from 55 to 93.5% by weight, particularly preferablyfrom 68 to 90% by weight, and from 0.1 to 30% by weight ofpolyfunctional aromatic amines (a2), in particular from 0.5 to 20% byweight, particularly preferably from 2 to 12% by weight, and from 5 to30% by weight of water (a3), in particular from 6 to 25% by weight,particularly preferably from 8 to 20% by weight.

The water content and the content of reactive isocyanate groups incomponent (a1) gives a theoretical content of amino groups, on theassumption of complete reaction of the water with the isocyanate groupsof component (a1) to form a corresponding amount of amino groups, wherethis content is added to the content resulting from component (a2)(total n^(amine)). The resultant usage ratio of the amount of NCO groupsn^(NCO) calculated as remaining, expressed as a ratio to the calculatednumber of amino groups formed, and also used, is hereinafter termedcalculated usage ratio n^(NCO)/n^(amine), and is an equivalence ratio,i.e. a molar ratio of the respective functional groups.

For the purposes of the abovementioned first variant, the calculatedusage ratio (equivalence ratio) n^(NCO)/n^(amine) can vary widely and inparticular can be from 0.6 to 5. It is preferable that n^(NCO)/n^(amine)is from 1 to 1.6, in particular from 1.1 to 1.4.

In a second, preferred variant, which comprises the use of water, thereaction of components (a1) to (a3) takes place in the presence of acatalyst (a5). In this second embodiment, it has proven advantageous touse from 0.1 to 15% by weight of water (a3), in particular from 0.2 to15% by weight, particularly preferably from 0.5 to 12% by weight, basedin each case on the total weight of components (a1) to (a3), which is100% by weight. Within the abovementioned ranges, particularlyadvantageous mechanical properties of the resultant porous materials areobtained, and this results from a particularly advantageous networkstructure. A larger amount of water has an adverse effect on the networkstructure and is disadvantageous with regard to the final properties ofthe porous material.

For the purposes of the preferred second variant, the ratio in whichabovementioned components (a1) to (a3) are used is preferably asfollows, in each case based on the total weight of components (a1) to(a3), which is 100% by weight: from 55 to 99.8% by weight of component(a1), in particular from 65 to 99.3% by weight, particularly preferablyfrom 76 to 97.5% by weight, and from 0.1 to 30% by weight ofpolyfunctional aromatic amine (a2), in particular from 0.5 to 20% byweight, particularly preferably from 2 to 12% by weight, and from 0.1 to15% by weight of water (a3), in particular from 0.2 to 15% by weight,particularly preferably from 0.5 to 12% by weight.

In the abovementioned second variant, the calculated usage ratio(equivalence ratio) n^(NCO)/n^(amine) is preferably from 1.01 to 5. Theequivalence ratio mentioned is particularly preferably from 1.1 to 3, inparticular from 1.1 to 2. In this embodiment, an excess of n^(NCO) withrespect to n^(amine) leads to less shrinkage of the porous material, inparticular xerogel, on removal of the solvent, and also, via synergisticaction together with the catalyst (a5), to an improved network structureand improved final properties of the resultant porous material.

In another second preferred embodiment, explained previously, thereaction of step (a) takes place in the absence of water. For thepurposes of this preferred embodiment, the ratio used of components (a1)and (a2) stated above is preferably as follows, based in each case onthe total weight of components (a1) and (a2), which is 100% by weight:from 20 to 80% by weight of component (a1), in particular from 25 to 75%by weight, particularly preferably from 35 to 68% by weight, and from 20to 80% by weight of component (a2), in particular from 25 to 75% byweight, particularly preferably from 32 to 65% by weight; no (a3).

For the purposes of this embodiment stated above, the usage ratio(equivalence ratio) n^(NCO)/n^(amine) is preferably from 1.01 to 5. Theequivalence ratio mentioned is particularly preferably from 1.1 to 3, inparticular from 1.1 to 2. Again, in this embodiment, an excess ofn^(NCO) with respect to n^(amine) leads to less shrinkage of the porousmaterial, in particular xerogel, on removal of the solvent, and also,via synergistic action together with the catalyst (a5), to an improvednetwork structure and improved final properties of the resultant porousmaterial.

The term organic gel precursors (A) is used hereinafter to covercomponents (a1) to (a3).

Component (a4)

The reaction of components (a1) and (a2) in the invention is carried outin the presence of at least one organic flame retardant as component(a4).

It is preferable that the flame retardants of component (a4) arecompounds comprising phosphorus and/or halogen, in particular bromine.However, it is also possible to use flame retardants based on boron.

Preferred amounts used of component (a4) are from 0.1 to 25% by weight,preferably from 1 to 15% by weight, based in each case on the totalweight of component (a1) to (a4), which is 100% by weight. This rangegives firstly particularly good flame retardancy properties and secondlyan advantageous pore structure. The preferred ranges mentioned apply toall of the embodiments stated at an earlier stage above in relation tocomponents (a1) to (a3).

It is preferable that component (a4) comprises at least one flameretardant which is selected from the group consisting of polybrominatedcompounds and organophosphorus compounds.

Polybrominated compounds are any of the compounds which comprise atleast two bromine atoms per molecule. Preferred polybrominated compoundsare in particular: pentabromotoluene, pentabromophenyl allyl ether,pentabromoethyl benzene, decabromobiphenyl, pentabromodiphenyl oxide,octabromodiphenyl oxide, decabromodiphenyl oxide,ethylenebis(tetrabromophthalimide), tetradecabromodiphenoxybenzene,ester-ethers of tetrabromophthalic anhydride, and tetrabromoneopentylglycol, and its derivatives.

Organophosphorus compounds are compounds which comprise at least onephosphorus atom and at least one carbon atom, in particular organicphosphates, phosphonates, phosphinates, phosphites, phosphonites,phosphinites, and phosphine oxides.

Organophosphorus compounds preferred for the purposes of the presentinvention are in particular those having a P═O double bond, inparticular organophosphates, organophosphonates, and organophosphineoxides. The prefix organo here characterizes the presence of an organiccompound in the abovementioned sense, and is not restricted to thepresence of a C—P bond.

The term organophosphate means organic compounds in which the P—OHgroups of phosphoric acid have been replaced by P—OR, where each R canbe identical or different and is mutually independently an organicmoiety, in particular a hydrocarbon group, which can be aliphatic,araliphatic, or aromatic, and which can comprise further functionalgroups.

The term organophosphonate means organic compounds in which the P—OHgroups of phosphonic acid have been replaced by P—OR and the P—H groupshave been replaced by P—R, where each R can be identical or differentand is mutually independently an organic moiety, in particular ahydrocarbon group, which can be aliphatic, araliphatic, or aromatic, andwhich can comprise further functional groups.

The term organophosphine oxide means organic compounds of the structureR₃P═O, where each R can be identical or different and is mutuallyindependently an organic moiety, in particular a hydrocarbon group,which can be aliphatic, araliphatic, or aromatic, and which can comprisefurther functional groups.

In one first preferred embodiment, component (a4) comprises at least oneorganophosphate. Preferred organophosphoric acid derivatives are thoseof the structure OP(OR)₃, where each R is mutually independently analiphatic, araliphatic, or aromatic hydrocarbon group having from 1 to20 carbon atoms, where this group can bear further functional groups,examples being ether linkages, halogen atoms, and also groups reactivetoward isocyanates, in particular OH groups and/or NH2 groups.

Preferred organophosphates are in particular triaryl and trialkylphosphates, e.g. diphenyl cresyl phosphate, tricresyl phosphate,triethyl phosphate, 2-ethylhexyl diphenyl phosphate, and the tetraphenylester of phenylene 1,3-phosphate, and also tris(2-chloropropyl)phosphate.

In another preferred embodiment, component (a4) comprises at least oneorganophosphonate.

Preferred organophosphonates are those of the structure RPO(OR)₂, whereeach R is mutually independently an aliphatic, araliphatic, or aromatichydrocarbon group having from 1 to 20 carbon atoms, where this group canbear further functional groups, examples being ether linkages, halogenatoms, and also groups reactive toward isocyanates, in particular OHgroups and/or NH₂ groups.

Preferred organophosphonates are in particular triaryl and trialkylphosphonates, diethyl N,N-bis(2-hydroxyethyl)aminomethylphosphonate,tetraalkyl diphosphonate compounds, dimethyl methanephosphonate, diethylethanephosphonate, and the like, and also phosphorus polyols andalkoxylated alkyl phosphonic acid derivatives.

In another preferred embodiment, component (a4) comprises at least oneorganophosphinic acid derivative.

Preferred organophosphine oxides are those of the structure OPR₃, whereeach R is mutually independently an aliphatic, araliphatic, or aromatichydrocarbon group having from 1 to 20 carbon atoms, where this group canbear further functional groups, examples being ether linkages, halogenatoms, and also groups reactive toward isocyanates, in particular OHgroups and/or NH₂ groups. Preferred organophosphine oxides are inparticular bis(hydroxymethyl)isobutylphosphine oxide,bis(3-hydroxypropyl) isobutylphosphine oxide, triethylphosphine oxide,dimethyldecylphosphine oxide, tributylphosphine oxide,tris(2-ethylhexyl)phosphine oxide, methyldiphenylphosphine oxide,trioctylphosphine oxide, triphenylphosphine oxide, andtris(2-methylphenyl)phosphine oxide.

Abovementioned flame retardants can be used individually or in the formof a combination of two or more of the abovementioned compounds.

As stated at an earlier stage above, the flame retardants can compriseone or more functional groups.

In one embodiment, it is preferable that component (a4) comprises atleast one compound which comprises a functional group reactive towardisocyanates, in particular at least 2 such reactive functional groups.Preferred reactive groups are OH and primary and secondary amino groups.Primary and secondary amino groups are reactive with respect tocomponent (a1) of the present invention and are thus incorporated intothe resultant network structure. Although OH groups are also reactivetoward isocyanates, this is true only to a relatively small extent, andany amines present are therefore reacted first. The reactivity of the OHgroups can be increased via use of a suitable catalyst (a5) whichaccelerates the urethane-formation reaction.

Particularly preferred flame retardants are as follows:tris(2-chloro-1-methylethyl) phosphate, diethyl ethylphosphonate,dimethyl propylphosphonate, tri(isopropylphenyl) phosphate (Reofos 95),oligomeric chloroalkyl phosphates (Fyrol 99), resorcinol bis(diphenylphosphates), 2-(2-hydroxyethoxy)ethyl 2-hydroxypropyl3,4,5,6-tetrabromophthalate, bis(hydroxymethyl)isobutylphosphine oxide,bis(3-hydroxypropyl) isobutylphosphine oxide, and trioctylphosphineoxide.

Catalyst (a5)

In one first preferred embodiment, the process of the invention ispreferably carried out in the presence of at least one catalyst ascomponent (a5).

Catalysts that can be used are in principle any of the catalysts whichare known to the person skilled in the art and which accelerate thetrimerization of isocyanates (these being known as trimerizatoncatalysts) and/or accelerate the reaction of isocyanates with aminogroups or OH groups (these being known as gel catalysts), and/or—to theextent that a component (a3), i.e. water, is used—accelerate thereaction of isocyanates with water (these being known as blowingcatalysts).

The corresponding catalysts are known per se, and perform in differentways in respect of the abovementioned three reactions. They can thus beallocated to one or more of the abovementioned types according toperformance. The person skilled in the art is moreover aware thatreactions other than the abovementioned reactions can also occur.

Corresponding catalysts can be characterized inter alia on the basis oftheir gel to blowing ratio, as is known by way of example fromPolyurethane [Polyurethanes], 3rd edition, G. Oertel, Hanser Verlag,Munich, 1993, pp. 104 to 110.

To the extent that no component (a3), i.e. no water, is used, preferredcatalysts have significant activity with regard to the trimerizationprocess. This has an advantageous effect on the homogeneity of thenetwork structure, resulting in particularly advantageous mechanicalproperties. To the extent that reactive (incorporatable) catalysts areused, preferred catalysts also have significant activity in respect ofcatalyzation of the urethane-formation reaction (gel reaction).

To the extent that water (a3) is used, preferred catalysts (a5) have abalanced gel to blowing ratio, so that the reaction of component (a1)with water is not excessively accelerated, adversely affecting thenetwork structure, with a simultaneous short gelling time, so thatdemolding time is advantageously small. Preferred catalystssimultaneously have significant activity with regard to thetrimerization process. This has an advantageous effect on thehomogeneity of the network structure, giving particularly advantageousmechanical properties.

The catalysts can be a monomer unit (incorporatable catalysts) or can benon-incorporatable.

It is advantageous to use the smallest effective amount of component(a5). It is preferable to use amounts of from 0.01 to 5 parts by weight,in particular from 0.1 to 3 parts by weight, particularly preferablyfrom 0.2 to 2.5 parts by weight, of component (a5), based on a total of100 parts by weight of components (a1) to (a4).

Catalysts preferred for the purposes of component (a5) are selected fromthe group consisting of primary, secondary, and tertiary amines,triazine derivatives, organometallic compounds, metal chelates,quaternary ammonium salts, ammonium hydroxides, and also the hydroxides,alkoxides, and carboxylates of alkali metals and of alkaline earthmetals.

Suitable catalysts are in particular strong bases, for examplequaternary ammonium hydroxides, e.g. tetraalkylammonium hydroxideshaving from 1 to 4 carbon atoms in the alkyl moiety andbenzyltrimethylammonium hydroxide, alkali metal hydroxides, e.g.potassium hydroxide or sodium hydroxide, and alkali metal alkoxides,e.g. sodium methoxide, potassium ethoxide and sodium ethoxide, andpotassium isopropoxide.

Other suitable catalysts are in particular alkali metal salts ofcarboxylic acids, e.g. potassium formate, sodium acetate, potassiumacetate, potassium 2-ethylhexanoate, potassium adipate, and sodiumbenzoate, and alkali metal salts of long-chain fatty acids having from 8to 20, in particular from 10 to 20, carbon atoms and optionally havingpendant OH groups.

Other suitable catalysts are in particular N-hydroxyalkyl quaternaryammonium carboxylates, e.g. trimethylhydroxypropylammonium formate.

Organometallic compounds are known per se to the person skilled in theart, in particular in the form of gel catalysts, and are likewisesuitable catalysts (a5). Organotin compounds, e.g. tin 2-ethylhexanoatesand dibutyltin dilaurates, are preferred for the purposes of component(a5).

Tertiary amines are known per se to the person skilled in the art as gelcatalysts and as trimerization catalysts. Tertiary amines areparticularly preferred as catalysts (a5). Preferred tertiary amines arein particular N,N-dimethylbenzylamine, N,N′-dimethylpiperazine,N,N-dimethylcyclohexylamine,N,N′,N″-tris(dialkylaminoalkyl)-s-hexahydrotriazines, e.g.N,N′,N″-tris(dimethylaminopropyl)-s-hexahydrotriazine,tris(dimethylaminomethyl)phenol, bis(2-dimethylaminoethyl) ether,N,N,N,N,N-pentamethyldiethylenetriamine, methylimidazole,1,2-dimethylimidazole, dimethylbenzylamine,1,6-diazabicyclo[5.4.0]undec-7-ene, triethylamine, triethylenediamine(IUPAC: 1,4-diazabicyclo[2,2,2]octane), dimethylaminoethanolamine,dimethylaminopropylamine, N,N-dimethylaminoethoxyethanol,N,N,N-trimethylaminoethylethanolamine, triethanolamine, diethanolamine,triisopropanolamine, and diisopropanolamine.

Catalysts particularly preferred for the purposes of component (a5) areselected from the group consisting of N,N-dimethylcyclohexylamine,bis(2-dimethylaminoethyl) ether,N,N,N,N,N-pentamethyldiethylenetriamine, methylimidazole,1,2-dimethylimidazole, dimethylbenzylamine,1,6-diazabicyclo[5.4.0]undec-7-ene,trisdimethylaminopropyihexahydrotriazine, triethylamine,tris(dimethylaminomethyl)phenol, triethylenediamine(diazabicyclo[2,2,2]octane), dimethylaminoethanolamine,dimethylaminopropylamine, N,N-dimethylaminoethoxyethanol,N,N,N-trimethylaminoethylethanolamine, triethanolamine, diethanolamine,triisopropanolamine, diisopropanolamine, metal acetylacetonates,ammonium ethylhexanoates, and ethylhexanoates of metal ions.

The use of the catalysts (a5) preferred for the purposes of the presentinvention leads to porous materials with improved mechanical properties,in particular to improved compressive strength. Use of the catalysts(a5) moreover reduces the gelling time, i.e. accelerates the gellingreaction, without any adverse effect on other properties.

Solvent

The reaction in the present invention takes place in the presence of asolvent.

For the purposes of the present invention, the term solvent comprisesliquid diluents, i.e. not only solvents in the narrower sense but alsodispersion media. The mixture can in particular be a genuine solution, acolloidal solution, or a dispersion, e.g. an emulsion or suspension. Itis preferable that the mixture is a genuine solution. The solvent is acompound that is liquid under the conditions of the step (a), preferablyan organic solvent.

Solvent used can in principle comprise an organic compound or a mixtureof a plurality of compounds, where the solvent is liquid under thetemperature conditions and pressure conditions under which the mixtureis provided in step (a) (abbreviated to: solution conditions). Theconstitution of the solvent is selected in such a way that the solventis capable of dissolving or dispersing, preferably dissolving, theorganic gel precursor. Preferred solvents are those which are a solventfor the organic gel precursor (A), i.e. those which dissolve the organicgel precursor (A) completely under reaction conditions.

The initial reaction product of the reaction in the presence of thesolvent is a gel, i.e. a viscoelastic chemical network swollen by thesolvent. A solvent which is a good swelling agent for the network formedin step (a) generally leads to a network with fine pores and with smallaverage pore diameter, whereas a solvent which is a poor swelling agentfor the gel resulting from step (a) generally leads to a coarse-porednetwork with large average pore diameter.

The selection of the solvent therefore affects the desired pore sizedistribution and the desired porosity. The selection of the solvent isgenerally also carried out in such a way as very substantially to avoidprecipitation or flocculation due to formation of a precipitatedreaction product during or after step (a) of the process of theinvention.

When a suitable solvent is selected, the proportion of precipitatedreaction product is usually smaller than 1% by weight, based on thetotal weight of the mixture. The amount of precipitated product formedin a particular solvent can be determined gravimetrically, by filteringthe reaction mixture through a suitable filter prior to the gel point.

Solvents that can be used are the solvents known from the prior art forisocyanate-based polymers. Preferred solvents here are those which are asolvent for components (a1) to (a5), i.e. those which substantiallycompletely dissolve the constituents of components (a1) to (a5) underreaction conditions. It is preferable that the solvent is inert, i.e.not reactive, toward component (a1).

Examples of solvents that can be used are ketones, aldehydes, alkylalkanoates, amides, such as formamide and N-methylpyrrolidone,sulfoxides, such as dimethyl sulfoxide, aliphatic and cycloaliphatichalogenated hydrocarbons, halogenated aromatic compounds, andfluorine-containing ethers. It is also possible to use mixtures made oftwo or more of the abovementioned compounds.

Acetals can also be used as solvents, in particular diethoxymethane,dimethoxymethane, and 1,3-dioxolane.

Dialkyl ethers and cyclic ethers are also suitable as solvent. Preferreddialkyl ethers are in particular those having from 2 to 6 carbon atoms,in particular methyl ethyl ether, diethyl ether, methyl propyl ether,methyl isopropyl ether, propyl ethyl ether, ethyl isopropyl ether,dipropyl ether, propyl isopropyl ether, diisopropyl ether, methyl butylether, methyl isobutyl ether, methyl tert-butyl ether, ethyl-n-butylether, ethyl isobutyl ether, and ethyl tert-butyl ether. Particularlypreferred cyclic ethers are tetrahydrofuran, dioxane, andtetrahydropyran.

Other preferred solvents are alkyl alkanoates, in particular methylformate, methyl acetate, ethyl formate, butyl acetate, and ethylacetate. Preferred halogenated solvents are described in WO 00/24799,page 4, line 12 to page 5, line 4.

Aldehydes and/or ketones are preferred solvents. Aldehydes or ketonessuitable as solvents are particularly those corresponding to the generalformula R²—(CO)—R¹, where R¹ and R² are hydrogen or alkyl groups having1, 2, 3 or 4 carbon atoms. Suitable aldehydes or ketones are inparticular acetaldehyde, propionaldehyde, n-butyraldehyde,isobutyraldehyde, 2-ethylbutyraldehyde, valeraldehyde, isopentaldehyde,2-methylpentaldehyde, 2-ethylhexaldehydes, acrolein, methacrolein,crotonaldehyde, furfural, acrolein dimer, methacrolein dimer,1,2,3,6-tetrahydrobenzaldehyde, 6-methyl-3-cyclohexenaldehyde,cyanacetaldehyde, ethyl glyoxylate, benzaldehyde, acetone, diethylketone, methyl ethyl ketone, methyl isobutyl ketone, methyl n-butylketone, ethyl isopropyl ketone, 2-acetylfuran,2-methoxy-4-methylpentan-2-one, cyclohexanone, and acetophenone. Theabovementioned aldehydes and ketones can also be used in the form ofmixtures. Particular preference is given, as solvents, to ketones andaldehydes having alkyl groups having up to 3 carbon atoms persubstituent. Ketones of the general formula R¹(CO)R² are veryparticularly preferred, where R¹ and R² are mutually independentlyselected from alkyl groups having from 1 to 3 carbon atoms. In one firstpreferred embodiment, the ketone is acetone. In another preferredembodiment, at least one of the two substituents R¹ and/or R² comprisesan alkyl group having at least 2 carbon atoms, in particular methylethyl ketone. Use of the abovementioned particularly preferred ketonesin combination with the process of the invention gives porous materialswith particularly small average pore diameter. Without any intention ofrestriction, it is believed that the pore structure of the resultant gelis particularly fine because of the relatively high affinity of theabovementioned particularly preferred ketones.

In many instances, particularly suitable solvents are obtained by usingtwo or more compounds which are selected from the abovementionedsolvents and which are completely miscible with one another.

In order, in step (a), to obtain an adequately stable gel which does notshrink markedly during the drying process in step (b), the proportion ofcomponents (a1) to (a4), based on the total weight of components (a1) to(a4) and on the solvent, which is 100% by weight, is generally notpermitted to be less than 5% by weight. It is preferable that theproportion of components (a1) to (a4), based on the total weight ofcomponents (a1) to (a4) and on the solvent, which is 100% by weight, isat least 6% by weight, particularly preferably at least 8% by weight, inparticular at least 10% by weight.

On the other hand, selection of an excessively high concentration ofcomponents (a1) to (a4) in the mixture provided is not permitted, sinceotherwise the product is not a porous material with advantageousproperties. The proportion of components (a1) to (a4), based on thetotal weight of components (a1) to (a4) and on the solvent, which is100% by weight, is generally at most 40% by weight. It is preferablethat the proportion of components (a1) to (a4), based on the totalweight of components (a1) to (a4) and on the solvent, which is 100% byweight, is at most 35% by weight, particularly at most 25% by weight, inparticular at most 20% by weight.

It is preferable that the proportion by weight of components (a1) to(a4), based on the total weight of components (a1) to (a4) and on thesolvent, which is 100% by weight, is in total from 8 to 25% by weight,in particular from 10 to 20% by weight, with particular preference from12 to 18% by weight. If the amount of the starting materials ismaintained within the range mentioned, porous materials are obtainedwith particularly advantageous pore structure, and with low thermalconductivity and low shrinkage during the drying process.

It is preferable that the reaction in step (a) of the process of theinvention is preceded by the provision of components (a1), (a2),optionally (a3), optionally (a5), and also (a3), and of the solvent.

It is preferable to provide, separately from one another, components(a1) on the one hand and (a2) and (a4), and also optionally (a3) andoptionally (a5) on the other hand, respectively in a suitable portion ofthe solvent. Separate provision permits ideal monitoring and/or controlof the gelling reaction prior to and during the mixing process.

To the extent that water is used as component (a3), it is particularlypreferable to provide component (a3) separately from component (a1).This avoids reaction of water with component (a1) with formation ofnetworks without the presence of component (a2). Otherwise, thepremixing of water with component (a1) leads to less advantageousproperties in relation to the homogeneity of pore structure and to thethermal conductivity of the resultant materials.

The mixture or mixtures provided prior to conduct of step (a) canmoreover comprise conventional auxiliaries known to the person skilledin the art, as further constituents. Examples that may be mentioned aresurfactant substances, nucleating agents, antioxidants, lubricants andmold-release aids, dyes and pigments, stabilizers, e.g. to counteractthe effects of hydrolysis, light, heat, or discoloration, inorganicand/or organic fillers, reinforcing agents, and biocides.

Further details concerning the abovementioned auxiliaries and additivescan be found in the technical literature, e.g. in Plastics AdditiveHandbook, 5th edition, H. Zweifel, ed. Hanser Publishers, Munich, 2001,pp. 104-127.

In order to carry out the reaction in step (a) of the process of theinvention, it is first necessary to produce a homogeneous mixture of thecomponents that are provided prior to the reaction in step (a).

The method of provision of the components reacted for the purposes ofstep (a) can be conventional. To this end, it is preferable to use astirrer or other mixing apparatus in order to achieve good and rapidmixing. In order to avoid defects in the mixing process, the time neededto produce the homogeneous mixture should be small in relation to thetime required for the at least partial formation of a gel by the gellingreaction. The other mixing conditions are generally not critical, and byway of example the mixing process can take place at from 0 to 100° C.and at from 0.1 to 10 bar (absolute), in particular by way of example atroom temperature and atmospheric pressure. Once production of ahomogeneous mixture has been achieved, the mixing apparatus ispreferably switched off.

The gelling reaction involves a polyaddition reaction, in particular apolyaddition process involving isocyanate groups and amino groups.

The term gel means a crosslinked system based on a polymer which is incontact with a liquid (a term used being solvogel or lyogel, or, withwater as liquid, aquagel or hydrogel). The polymer phase here forms acontinuous three-dimensional network.

For the purposes of step (a) of the process of the invention, the gel isusually produced by allowing the material to stand, e.g. simply allowingthe container, reaction vessel, or reactor within which the mixture ispresent (hereinafter termed gelling apparatus) to stand. It ispreferable that the mixture is not subjected to further stirring ormixing during the gelling process (gel formation process), since thiscould inhibit formation of the gel. It has proven advantageous to coverthe mixture during the gelling process or to seal the gelling apparatus.

The gelling process is known per se to the person skilled in the art andis described by way of example in WO-2009/027310, page 21, line 19-page23, line 13.

Step (b)

In step (b) in the invention, the gel obtained in the previous step isdried, by removing the organic solvent to give the organic porousmaterial.

In principle it is possible to use a drying process under supercriticalconditions, preferably after replacement of the solvent by CO₂ or byother solvents suitable for supercritical drying purposes. This type ofdrying process is known per se to the person skilled in the art.Supercritical conditions characterize a temperature and a pressure atwhich the fluid phase to be removed is in the supercritical state. Thismethod can reduce the shrinkage of the gel product during removal of thesolvent. The material obtained from the supercritical drying process istermed aerogel.

However, for simple conduct of the process it is preferable to dry thegels by converting the liquid comprised within the gel to the gaseousstate at a temperature and a pressure below the critical temperature andthe critical pressure of the liquid comprised within the gel. Thematerial obtained from the subcritical drying process is termed xerogel.

It is preferable that the gel is dried by converting the solvent to thegaseous state at a temperature and a pressure below the criticaltemperature and the critical pressure of the solvent. There isaccordingly preferably no prior replacement by another solvent beforethe drying process removes the solvent that was present during thereaction.

Appropriate methods are likewise known to the person skilled in the artand are described in WO-2009/027310, page 26, line 22-page 28, line 36.

Shrinkage of the gel product is particularly apparent in the subcriticaldrying process. Minimization of shrinkage during the drying process isan advantage of the present invention.

Properties of the porous materials and use

The present invention further provides the porous materials obtainablein the process of the invention.

Xerogels are preferred as porous materials for the purposes of thepresent invention, and this means that the porous material obtainable inthe invention is preferably a xerogel.

For the purposes of the present invention, a xerogel is in particular aporous material with porosity of at least 70% by volume and withvolume-average pore diameter of at most 50 micrometers, produced via asol-gel process, where the liquid phase has been removed from the gelvia drying below the critical temperature and below the criticalpressure of the liquid phase (“subcritical conditions”).

For the purposes of the present invention, average pore size ispreferably determined by means of mercury porosimetry to DIN 66133(1993) at room temperature. For the purposes of this invention, averagepore size is equivalent to average pore diameter. Volume-average porediameter is determined here by calculation from the pore sizedistribution determined to the abovementioned standard.

The volume-average pore diameter of the porous material is preferably atmost 8 micrometers. The volume-average pore diameter of the porousmaterial is particularly preferably at most 5 micrometers, veryparticularly preferably at most 3 micrometers, and in particular at most1 micrometer.

Although minimum pore size, with high porosity, is desirable in order togive low thermal conductivity, there is a practical lower limit forvolume-average pore diameter resulting from the production process andfrom the need to obtain a porous material with adequate mechanicalstability. The volume-average pore diameter is generally at least 50 nm,preferably at least 100 nm. In many instances, volume-average porediameter is at least 200 nm, in particular at least 300 nm.

The porosity of the porous material obtainable in the invention ispreferably at least 70% by volume, in particular from 70 to 99% byvolume, particularly preferably at least 80% by volume, veryparticularly preferably at least 85% by volume, in particular from 85 to95% by volume. Porosity in % by volume means that the specifiedproportion of the total volume of porous material is composed of pores.Although maximum porosity is mostly desirable in order to obtain minimumthermal conductivity, mechanical properties, and the processability ofthe porous material, place an upper limit on porosity.

Components (a1), optionally to some extent first reacted with water, and(a2) are in reacted (polymeric) form in the porous material obtainablein the invention. By virtue of the composition of the invention, themonomer units (a1) and (a2) are predominantly present in a form bondedby way of urea linkages and/or by way of isocyanurate linkages withinthe porous material, and the isocyanurate groups here are produced viatrimerization of isocyanate groups of the monomer units (a1). To theextent that the porous material comprises further components, otherpossible linkages are by way of example urethane groups, where these areproduced via reaction of isocyanate groups with alcohols or withphenols.

It is preferable that, within the porous material, components (a1),optionally to some extent first reacted with water, and (a2) are presentin a form which to an extent of at least 50 mol % has been linked viaurea groups —NH—CO—NH— and/or by way of isocyanurate linkages. It ispreferable that, within the porous material, components (a1) and (a2)are present in a form linked to an extent of from 50 to 100 mol % viaurea groups and/or by way of isocyanurate linkages, in particular to anextent of from 60 to 100 mol %, very particularly preferably to anextent of from 70 to 100 mol %, in particular to an extent of from 80 to100 mol %, for example to an extent of from 90 to 100 mol %.

The balancing mol % value required to give 100 mol % represents otherlinkages, and these other linkages are known per se to the personskilled in the art in the field of isocyanate polymers. Examples thatmay be mentioned are ester groups, urea groups, biuret groups,allophanate groups, carbodiimide groups, uretdione groups and/orurethane groups.

The mol % values for the linkages of the monomer units within the porousmaterial are determined by means of NMR spectroscopy (nuclear spinresonance) in the solid state or in the swollen state. Suitable methodsof determination are known to the person skilled in the art.

The density of the porous material obtainable in the invention isusually from 20 to 600 g/l, preferably from 50 to 500 g/l, andparticularly preferably from 70 to 200 g/l.

The process of the invention gives a coherent porous material, and notmerely a polymer powder or polymer particles. The three-dimensionalshape of the resultant porous material here is determined via the shapeof the gel, and this shape is in turn determined via the shape of thegelling apparatus. By way of example, therefore, a cylindrical gelcontainer usually gives an approximately cylindrical gel, which can thenbe dried to give a porous material in the shape of a cylinder.

The porous materials obtainable in the invention have low thermalconductivity, high porosity, and low density, together with highmechanical stability, and also good flame retardancy properties. Theporous materials moreover have low average pore size. The combination ofthe abovementioned properties permits use as insulation material in thethermal insulation sector, in particular for applications in the vacuumsector, where preference is given to minimum thickness of vacuum panels,for example in refrigeration equipment or in buildings. Preference istherefore given to the use in vacuum insulation panels, in particular ascore material for vacuum insulation panels. Preference is also given tothe use of the porous materials of the invention for thermal insulation,in particular in construction applications. The materials obtainable viathe present invention feature firstly advantageous thermalconductivities and secondly advantageous flame retardancy properties.The advantageous thermal insulation properties at atmospheric pressuretogether with the good flame retardancy properties make the materials ofthe invention particularly suitable for construction applications.

EXAMPLES

Pore volume in ml per g of sample and average pore size of the materialswere determined by means of mercury porosimetry to DIN 66133 (1993) atroom temperature. For the purposes of this invention, average pore sizeis equivalent to average pore diameter. Volume-average pore diameter isdetermined here by calculation from the pore size distributiondetermined to the abovementioned standard.

Porosity in % by volume was calculated from the formula P=(V_(i)/(V_(i)+V_(s)))*100% by volume, where P is the porosity, V_(i) is the Hgintrusion volume to DIN 66133 in ml/g, and V_(s) is the specific volumein ml/g of the test specimen.

Density ρ of the porous gel in g/ml was calculated from the formulaρ=m/(π*r²)*h, where m is the mass of the porous gel, r is the radius(half diameter) of the porous gel, and h is the height of porous gel.

Shrinkage during step (b) of the process of the invention was determinedby comparing the height of a cylindrical gel and the diameter in cmprior to and after removal of the solvent. The values stated are basedon the relative volume of the cylinder after shrinkage in comparisonwith the gel product prior to removal of the solvent, and this meansthat shrinkage is stated as % loss of volume. Prior to shrinkage, theheight of the cylinders was 4.9 cm and the diameter of the cylinders was2.7 cm.

Flame retardancy properties were determined by the BKZ test as describedabove. To the extent that the maximum flame height stated for thepurposes of combustibility class 5, 15 cm, was not achieved, the flameheight observed in the BKZ test has instead been stated.

The following compounds were used:

Component a1:

Oligomeric MDI (Lupranat® M50) having NCO content of 31.5 g per 100 g toASTM D5155-96 A, functionality in the range from 2.8 to 2.9, andviscosity of 550 mPa·s at 25° C. to DIN 53018 (hereinafter “compoundM50”).

Component a2:

Oligomeric diaminodiphenylmethane with viscosity of 2710 mPa·s at 50° C.to DIN 53018, functionality in the region of 2.4, and amino groupcontent of 9.93 mmol/g (hereinafter “PMDA”).

Component a3:

PHT-4-Diol™ from Chemtura:

Antiblaze® V490 from Albemarle:

Example 1

2.0 g of compound M50 were dissolved in 10.5 g of acetone in a glassbeaker at 20° C., with stirring. 1.3 g of PMDA and 0.5 g of Exolit®OP560 were dissolved in 11 g of acetone in a second glass beaker. Thetwo solutions of step (a) were mixed. This gave a clear mixture of lowviscosity. The mixture was allowed to stand at room temperature for 24hours for hardening. The gel was then removed from the glass beaker, andthe liquid (acetone) was removed by drying at 20° C. for 7 days.

The average pore diameter of the resultant material was 4.0 μm. Porositywas 86% by volume, with corresponding density of 233 g/l. Shrinkage was42%. The flame height measured in the BKZ test was 5 cm.

Example 2

2.0 g of compound M50 were dissolved in 10.5 g of acetone in a glassbeaker at 20° C., with stirring. 1.3 g of PMDA and 0.5 g of PHT-4-Diol™were dissolved in 11 g of acetone in a second glass beaker. The twosolutions of step (a) were mixed. This gave a clear mixture of lowviscosity. The mixture was allowed to stand at room temperature for 24hours for hardening. The gel was then removed from the glass beaker, andthe liquid (acetone) was removed by drying at 20° C. for 7 days.

The average pore diameter of the resultant material was 5.0 μm. Porositywas 85% by volume, with corresponding density of 235 g/l. Shrinkage was43%. The flame height measured in the BKZ test was 9 cm.

Example 3

2.0 g of compound M50 were dissolved in 10.5 g of acetone in a glassbeaker at 20° C., with stirring. 1.3 g of PMDA and 0.5 g of Antiblaze®V490 from Albemarle were dissolved in 11 g of acetone in a second glassbeaker. The two solutions of step (a) were mixed. This gave a clearmixture of low viscosity. The mixture was allowed to stand at roomtemperature for 24 hours for hardening. The gel was then removed fromthe glass beaker, and the liquid (acetone) was removed by drying at 20°C. for 7 days.

The average pore diameter of the resultant material was 3.0 μm. Porositywas 86% by volume, with corresponding density of 226 g/l. Shrinkage was42%. The flame height measured in the BKZ test was 5 cm.

Example 4 comp.

2.4 g of compound M50 were dissolved in 10.5 g of acetone in a glassbeaker at 20° C., with stirring. 1.3 g of compound PMDA were dissolvedin 11 g of acetone in a second glass beaker. The two solutions of step(a) were mixed. This gave a clear mixture of low viscosity. The mixturewas allowed to stand at room temperature for 24 hours for hardening. Thegel was then removed from the glass beaker, and the liquid (acetone) wasremoved by drying at 20° C. for 7 days.

When the resultant material was compared with example 1, it had amarkedly shrunk shape. Shrinkage was 70%. Porosity was 71% by volume,with corresponding density of 390 g/l. The flame height measured in theBKZ test was 7 cm, and it should be noted here that combustibility isreduced by the high density of the material.

1. A process for producing porous materials comprising the followingsteps: (a) reacting at least one polyfunctional isocyanate (a1) and atleast one polyfunctional aromatic amine (a2) in an organic solventoptionally in the presence of water as component (a3) and optionally inthe presence of at least one catalyst (a5); and then (b) removing theorganic solvent to obtain the organic porous material, where step (a) iscarried out in the presence of at least one organic flame retardant ascomponent (a4), where this flame retardant is soluble in the solvent. 2.The process according to claim 1, where the flame retardants ofcomponent (a3) are compounds comprising phosphorus and/or halogen, inparticular bromine.
 3. The process according to claim 1 or 2, where theamounts used as component (a4) are from 0.1 to 25% by weight, preferablyfrom 1 to 15% by weight, based in each case on the amount by weight ofcomponents (a1) to (a4), which is 100% by weight.
 4. The processaccording to one or more of claims 1 to 3, where component (a4)comprises at least one flame retardant selected from the groupconsisting of polybrominated compounds and of organophosphoruscompounds.
 5. The process according to one or more of claims 1 to 4,where component (a4) comprises at least one organophosphoric acidderivative.
 6. The process according to one or more of claims 1 to 5,where component (a4) comprises at least one organophosphonic acidderivative.
 7. The process according to one or more of claims 1 to 6,where component (a4) comprises at least one organophosphinic acidderivative.
 8. The process according to one or more of claims 1 to 7,where component (a4) comprises at least one compound which comprises afunctional group reactive toward isocyanates, in particular at least 2such reactive functional groups.
 9. The process according to one or moreof claims 1 to 8, where the at least one polyfunctional isocyanate (a1)is composed of at least one polyfunctional isocyanate selected fromdiphenylmethane 4,4′-diisocyanate, diphenylmethane 2,4′-diisocyanate,diphenylmethane 2,2′-diisocyanate, and oligomeric diphenylmethanediisocyanate.
 10. The process according to one or more of claims 1 to 9,where component (a1) comprises oligomeric diphenylmethane diisocyanateand its functionality is at least 2.4.
 11. The process according to oneor more of claims 1 to 10, where component (a2) comprises oligomericdiaminodiphenylmethane and its functionality is at least 2.4.
 12. Theprocess according to one or more of claims 1 to 11, where the at leastone polyfunctional aromatic amine comprises at least one polyfunctionalaromatic amine of the general formula I

where R¹ and R² can be identical or different and are selected mutuallyindependently from hydrogen and linear or branched alkyl groups havingfrom 1 to 6 carbon atoms, and where all of the substituents Q¹ to Q⁵ andQ¹ to Q⁵′ are identical or different and are selected mutuallyindependently from hydrogen, a primary amino group, and a linear orbranched alkyl group having from 1 to 12 carbon atoms, where the alkylgroup can bear further functional groups, with the proviso that thecompound of the general formula I comprises at least two primary aminogroups, where at least one of Q¹, Q³, and Q⁵ is a primary amino group,and at least one of Q¹′, Q³′, and Q⁵′ is a primary amino group.
 13. Theprocess according to claim 12, where Q², Q⁴, Q²′, and Q⁴′ are selectedin such a way that the compound of the general formula I has at leastone linear or branched alkyl group which can bear further functionalgroups and which has from 1 to 12 carbon atoms in α-position withrespect to at least one primary amino group bonded to the aromatic ring.14. The process according to one or more of claims 1 to 13, wherecomponent (a2) comprises at least one of the following compounds:4,4′-diaminodiphenyl-methane, 2,4′-diaminodiphenylmethane,2,2′-diaminodiphenylmethane, and oligomeric diaminodiphenylmethane. 15.The process according to one or more of claims 1 to 14, where thereaction takes place in the presence of a catalyst (a5).
 16. The processaccording to one or more of claims 1 to 15, where the removal of thesolvent takes place via conversion of the solvent to the gaseous stateat a temperature and a pressure below the critical temperature and thecritical pressure of the solvent.
 17. A porous material obtainableaccording to claims 1 to
 16. 18. The porous material according to claim17, where the volume-average pore diameter of the xerogel is at most 5micrometers.
 19. The use of the porous material according to claim 17 or18 for thermal insulation.
 20. The use of the porous material accordingto claim 17 or 18 for thermal insulation in construction applications.